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A-LevelMathematicsProbability and statistics9709/62 · Feb/Mar 2018 · Q46 Marks

The discrete random variable X has the following probability distribution. X|-2|0|1|3|4 P(X = x)|0.2|0.1|p|0.1|q

  1. (i)Given that E(X) = 1.7, find the values of p and q.[4]
  2. (ii)Find Var(X).[2]

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2018). The mark or mark type is shown in brackets.

  1. [M1] Unsimplified sum of probabilities equated to 1
  2. [M1] Unsimplified Sum of px equated to 1.7
  3. [M1] Solve simult. equations to find expression in p or q
  4. [A1]
  5. [M1] Use correct unsimplified expression for variance
  6. [A1]

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About this question

Topic
Probability and statistics, A-Level Mathematics (syllabus 9709). Structured question, 6 marks.
Source
A-Level Mathematics, Feb/Mar 2018 Paper 6 Variant 2, question 4.

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